Upload the Easy Plugin for AdSense plugin (the whole easy-adsense folder) to the '/wp-content/plugins/' directory.

Activate the plugin through the 'Plugins' menu in WordPress.

Go to the Setup -> Easy Plugin for AdSense and enter your AdSense code and options.

Go to Themes -> Widgets to add widgets to your side bar(s).

Tips

Although the Easy Plugin for AdSense plugin is designed to handle Google AdSense efficiently, there is nothing preventing you from using the text boxes to place any other kind of text in your blog posts and pages. In particular, you can use ad text from other providers, especially in the header and footer.